In this technical field, a LTE (Long Term Evolution) scheme is being discussed in a W-CDMA standardization organization 3GPP as a successor communication scheme of a W-CDMA (Wideband-Code Division Multiple Access) scheme, a HSDPA (High Speed Downlink Packet Access) scheme and a HSUPA (High Speed Uplink Packet Access) scheme. In the LTE scheme, an inactive (idle) user apparatus may migrate between cells while performing DRX (Discontinuous Reception) and is managed for each TA (Tracking Area) including one or more cells while maintaining the latest location registration state. On the other hand, a base station conducts DTX (Discontinuous Transmission) in downlinks for that user apparatus so that the user apparatus can conduct the DRX properly. In accordance with the LTE scheme, an active user apparatus may also conduct the DRX as needed mainly in terms of battery energy savings.
A user apparatus conducting the DRX switches between an active state and an inactive state in fixed cycles (DRX cycle) and receives L1/L2 control signals at the cycles. The user apparatus demodulates the L1/L2 control signals and determines whether there is information destined for the user apparatus. The information may include the presence of downlink data, a resource block and a data format such as a data modulation scheme to be used if the downlink data is present, and a resource block and a data format available for the next uplink data transmission. If information destined for the user apparatus is present, the user apparatus may receive downlink data in accordance with the information. Otherwise, the user apparatus may transition from the active state to the inactive state and wait for the next activation timing. In general, a longer DRX cycle leads to greater effect on the battery savings or power consumption. However, it should be noted that the DRX may affect QoS (Quality of Service). Some techniques for setting the DRX cycle for each radio bearer are disclosed in 3GPP R2-070463, Feb. 6, 2007, for example.
Many user apparatuses conducting the DRX can be arranged to activate in different subframes.
FIG. 1 illustrates ten types of activation timing patterns (patterns 1-10) for a certain DRX cycle. User apparatuses conduct the DRX in accordance with any of these patterns. For any pattern, the user apparatus is active during one TTI and inactive during nine TTIs. The many user apparatuses are arranged not to concentrate on a certain pattern. For example, if the user apparatuses are associated with patterns 1-10, patterns 1, 2, . . . , 10 may be cyclically assigned to the user apparatuses. Alternatively, any of patterns 1-10 may be randomly used. Alternatively, a remainder of division of an identification number of a user apparatus by 10, for example, C-RNTI mod 10, may be used as the pattern number. Even in any of the cases, the user apparatuses are distributed over all patterns 1-10.
A limited amount of resources can be used for L1/L2 control channels and data signals, and accordingly a limited number of user apparatuses are allowed (scheduled for) transmissions in a single radio frame. As a result, as illustrated in the upper side of FIG. 2, if a smaller number of user apparatuses belong to a certain pattern, there would be a higher likelihood that resource blocks may be assigned for transmissions of downlink data (shared data channels). On the other hand, as illustrated in the lower side of FIG. 2, if a larger number of user apparatuses belong to a certain pattern, there would be a lower likelihood that resource blocks may be assigned for transmissions of downlink data (shared data channels). If data and control signals desired to be transmitted to a user apparatus at a DRX activation timing are not scheduled, the transmission of the data and control signals destined for the user apparatus would be delayed to the next activation timing.
On the other hand, the user apparatuses ubiquitously reside within a service area and are in various communication environments. Thus, even if the user apparatuses receive the same radio bearer, the user apparatuses may have different channel states and different radio transmission states.
There is a high risk that a user apparatus with a poor channel state, such as a user apparatus residing in a cell boundary, may fail to receive a downlink L1/L2 control signal and a subsequent data signal. If the user apparatus fails to receive the downlink signals, the user apparatus cannot be communicating until the next activation timing, resulting in longer transmission delay of the downlink signals. This may be more significant for a longer DRX cycle. Particularly, the user apparatus residing in a cell boundary may fail to receive the downlink signals with a high likelihood compared to a user apparatus residing near abase station. When the user apparatus residing in a cell boundary is communicating information associated with handover control, it is undesirable to make the above transmission delay longer.